如何在python中将MPI信息传递给ctypes

问题描述

我的动机是将MPI信息有效地从python传递到通过ctypes调用的C函数.我在python中将mpi4py用于MPI绑定.我想通过一个用C编写并通过python中的ctypes调用的简单MPI示例代码来学习它.我已经详细说明了在下面运行时遇到的步骤和错误.

My motivation is to pass MPI information effectively from python to C functions invoked through ctypes. I used mpi4py for MPI bindings in python. I would like to learn it through a simple example MPI code written in C and invoked through ctypes in python. I have detailed the steps and the error that I get while running below.

C代码 [ passMpi4Py.c ]

#include <stdio.h>
#include <mpi.h>

void sayhello(MPI_Comm comm)
{
  int size, rank;
  MPI_Comm_size(comm, &size);
  MPI_Comm_rank(comm, &rank);
  printf("Hello, World! "
         "I am process %d of %d.\n",
         rank, size);
}

我用gcc/openmpi-1.6编译了上面的c代码，如下所示:

I compiled the above c code with gcc/openmpi-1.6 as follows:

mpicc -shared -Wl，-soname，passMpi4Py -o passMpi4Py.so -fPIC passMpi4Py.c

Python包装器 [ passMpi4PyWrapper.py ]

import ctypes
from mpi4py import MPI
testlib = ctypes.CDLL('path-to-file/passMpi4Py/passMpi4Py.so')

testlib.sayhello(MPI.COMM_WORLD)

当我尝试通过运行以上代码时

When i try to run the above code by using

mpirun -np 4 python passMpi4PyWrapper.py

我收到以下错误

Traceback (most recent call last):
Traceback (most recent call last):
  File "passMpi4PyWrapper.py", line 5, in <module>
Traceback (most recent call last):
  File "passMpi4PyWrapper.py", line 5, in <module>
  File "passMpi4PyWrapper.py", line 5, in <module>
Traceback (most recent call last):
    testlib.sayhello(MPI.COMM_WORLD)
ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know how to convert parameter 1
    testlib.sayhello(MPI.COMM_WORLD)
ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know how to convert parameter 1
    testlib.sayhello(MPI.COMM_WORLD)
ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know how to convert parameter 1
  File "passMpi4PyWrapper.py", line 5, in <module>
    testlib.sayhello(MPI.COMM_WORLD)
ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>: Don't know how to convert parameter 1

更新:

在C程序MPI函数中使用* MPI_COMM_WORLD *代替 comm ，可以帮助我消除错误.但是，我仍然想知道这是否是将MPI信息传递给C程序的最佳方法.

Using *MPI_COMM_WORLD* instead of comm in the C program MPI functions helps me to remove the error. However I still would like to know if this is the best possible way to pass MPI information to a C program.

推荐答案

您缺少一种将Python的MPI.COMM_WORLD(这是mpi4py的Comm类的实例)映射到MPI_COMM_WORLD(这是一个int句柄)的方法. .这可以通过使用SWIG生成包装器来完成. mpi4py教程具有与您基本相同的示例，但添加了SWIG接口文件.

You are missing a way to map Python's MPI.COMM_WORLD (which is an instance of the mpi4py's Comm class) to MPI_COMM_WORLD (which is an int handle). This can be done by generating a wrapper with SWIG. The mpi4py tutorial has basically the same example as you have, but with the SWIG interface file added.

如果不想使用SWIG，则可以用C代码执行转换.如果查看SWIG示例正在导入的文件mpi4py.i，可以看到使用PyMPIComm_Get完成了转换. mpi4py源带有未使用的示例SWIG .

If you'd rather not use SWIG, you can perform the conversion in the C code. If you look at the file mpi4py.i that the SWIG example is importing, you can see that conversion is done with PyMPIComm_Get. mpi4py source comes with an example that does not use SWIG.

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